# Fuse Size?

Clean Install
Silver - Posts: 446
Joined: January 03, 2004
Location: United States
Posted: December 05, 2006 at 9:09 PM / IP Logged

hahah this one became funny.... but i have a ? for ya DYON

this is the first honestly that i have heard find a fuse according to the wire gauge..."interesting to me"

what ever happend to take the RMS divide by alternator output at idle ?

thanks man just wanted to ask ;) its been along time since i have seen yalls names ;) good to see yall agian

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haemphyst
Platinum - Posts: 5,052
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 06, 2006 at 8:58 AM / IP Logged
Here's the answer to that, and it's PERFECT:
stevdart wrote:

master5 wrote:
 ..if the system called for a 4ga wire..and we used a zero gauge..is it understood that we should intentionally put in a larger fuse then required soley based on the wire gauge and not based on the systems maximum draw potential?

The consideration of fuse value is based on the gauge of the wire it protects. If the fuse is NOT chosen with this consideration, other influences were allowed to interfere with the reasoning process.

Why use a fuse or breaker value of 300 to 350 amps on that 1/0 wire if the pull of the gear doesn't support such a large value? You have to answer this yourself with the simple question: Why is there a 1/0 wire installed when all that was needed was 4 gauge? That's an example of faulty reasoning based on the wrong consideration; it's based on the pull of the equipment, not the wire size. Or is it the associated cost of the fuse or breaker that prompts the choice in fuse value? There again, invalid reasoning. And how valid is that 1/0 wire anyway when you've installed a 4 ga. eqivalent fuse in the run? ...or with a breaker that will shut off when the thermal limits of a 4 ga. wire has been reached?

The intent here is to provide the basic principles of why and how. It should be known that the fuse protects the wire, and any mention of the current system's demand on the fuse's ability should not be addressed as it has no bearing on the principle of this wire/fuse safety system.    A professionally-installed system should always have the correct safety devices in place for the wires they serve.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice.﻿ You should write it down."
master5
Silver - Posts: 1,123
Joined: October 10, 2006
Location: United States
Posted: December 08, 2006 at 9:45 AM / IP Logged

ok ,perfectly understood as well. but back when I worked at a shop that basically did 90% competition vehicles we would often use zero gauge when a 2ga or even 4ga would have sufficed. This never caused any harm, it looked great (well massive wire always does) and the judges appreciated it.

But if the systems demands were lets say for example, 125amp ,I would see no reason to install a 350a fuse..even though according to some here the wire "calls" for it.

In anyone elses opinion, was this improper or unsafe in any way? Keep in mind I am aware that a wire this large was "unnessesary" perhaps..but aside from the other listed  benifits of this "overkill"..it added nicely to our profit margin using the larger wire, distribution blocks and terminals.

DYohn
Moderator - Posts: 10,735
Joined: April 22, 2003
Location: Arizona, United States
Posted: December 08, 2006 at 9:54 AM / IP Logged

master5, like I said before, the fuse is to protect the wire and one should size a fuse with the capabilities of the wire in mind.  If the wire is capable of carrying 350 amps, then the purpose of the fuse is to prevent MORE THAN 350 amps from being carried by the wire.  This does not mean you NEED a 350 amp fuse, just that you must not allow more than that.  Will your 125 amp fuse do this job?  Sure.  It's called being logical and understanding electrical safety requirements.

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master5
Silver - Posts: 1,123
Joined: October 10, 2006
Location: United States
Posted: December 08, 2006 at 10:26 AM / IP Logged

Thanks for the response, understood

arlin22
Member - Posts: 8
Joined: December 16, 2006
Location: United States
Posted: December 18, 2006 at 9:38 AM / IP Logged

I'll chime in with a question related to a DIY build up 'cause i am at this stage, and you all seem to know the right answer.  I am installing a PDX 1.1000 amp right now and the wiring will probably be 4 ga at the amp.  however, I intend to add another PDX 2.150 or 4.150 later (3 months or less) and don't want to re do the wiring later.  i would like to understand what my 'best' method to power the sub amp now and future amp(s) later will be for wiring.  I am going to assume that the best should be to run 2 ga from the battery now (fused for wire size) to a 2 -4 output distribution block that can run 4 ga out to the amp(s).  Then I can run additional wiring from the dist block later as I require it.  Grounding will be the same ( I assume).  Is there anything technically wrong with this?  I am trying to avoid running wire twice and damaging my interior components by removing and replacing them over and over.  Also, buying wire twice (cost is always a factor :)  ) .

thanks.

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Techmaster
Member - Posts: 42
Joined: December 01, 2003
Location: United States
Posted: January 09, 2007 at 8:36 PM / IP Logged
That's actually a great idea, and I'm basically doing the same with mine. I will have 4ga going back to the trunk, to a fused distribution block. From there, I can add 8ga wires and appropriate fuses to run to any additional amps or whatever I install down the road. For now it will go from 4ga to a single 8ga for my sub amp, but I'm adding a small 4ch amp for the highs and I can simply tap into that distribution block for power, rather than running a wire through the firewall again. I *hate* penetrating firewalls, especially on a volvo chassis where the thing is heavily reinforced. Luckily my car has a rubber boot where the manual models have a clutch pedal, but still... It's under the battery, so it's not fun. It will be nice to run one wire and be done with it. Also, I'm going to run some fans off the distribution block. It should be a very convenient way of doing things.
master5
Silver - Posts: 1,123
Joined: October 10, 2006
Location: United States
Posted: January 10, 2007 at 11:15 AM / IP Logged

Yep same here.  Basically I "pre-plan" for upgrades by installing a 4ga. or larger and using a distribution block. This way in the future when I add more power..or additonal amps etc. the main wire is already ran saving time and effort.

I will generally use a main fuse based on the power consumption of the device(s) connected to it..although I totally understand the premise of wire size being the determining factor. Once I perform the upgrades I will use the appropriate fuse(s) but I will never use a fuse with a rating that exceeds what the wire gauge can handle...or a wire gauge not up to task..I hope I did not give that impression.

rodney_rude_1
Member - Posts: 11
Joined: March 07, 2007
Location: Australia
Posted: March 07, 2007 at 11:47 PM / IP Logged

hey all.

the wiring kit i recently purchased (absolute AB-404, 4 gage amp instalation kit) has a 60A fuse for the main power line.

now..the amplifier i have is 1600watt RMS (5000 watt MAX, although not relevant) which is using the 4 gage wire for power (duh)

should i get a 150A fuse to replace the 60A????

cheers

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master5
Silver - Posts: 1,123
Joined: October 10, 2006
Location: United States
Posted: March 08, 2007 at 11:53 AM / IP Logged

I would say that is a definate yes.

However for an amp with that kind of power a 2ga. minimum may be called for depending on the final ohms load. But regardless I couldn't imagine a 60a fuse lasting the first heavy bass note with that amp.

Good Luck.

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